This invention relates to a high-capacity optical recording medium, such as CD-I, CDV or DVD-R (digital video disk-recordable or digital versatile disk-recordable), which is capable of recording and reproducing data by means of a laser beam.
Recently, an increase in the amount of information, data demands a high-density storage media which permits a recording/playback of a vast amount of information rapidly. Thus, as next-generation high-capacity disc systems, development of DVD-R are currently investigated on various aspects such as recording materials capable of using very small recording pits, image compression technique such as MPEG2 (motion picture experts group), and laser diodes emitting light having short wavelength for reading small recorded pits.
As for the laser diodes emitting light in the red region, AlGaInP laser diodes, which emit light having a wavelength of 670 nm, have been developed for commercial operation and used for bar code readers and measuring instruments. With the capacity of optical discs increased, red color laser diodes have been used in the optical data storage field. In a case of DVD drives, light within the 630-670 nm band, which is emitted by laser diodes, is standardized as a light source. As for the read-only DVD-ROM (digital video disc-read-only-memory) drives, drives using light having a wavelength of 650 nm or less are marketed.
In this circumstance, DVD-Rs capable of recording and reproducing data with a laser beam having a wavelength of 630-670 nm and having excellent light resistance, storage stability and surface uniformity are desired. Until now, however, such DVD-Rs have not yet been developed.
Land prepit format using a land prepit signal (Lppb) of 0.16-0.32 has been generally adopted for DVD-R format. This method, however, has a problem because the cutting width of the recording material should be finely controlled using a finely fabricated stamper, etc.
The storage capacity of optical disk devices can be increased by employing a constant linear velocity (CLV) method. The CLV method, however, needs a slow access time. The access time can be shorten by employing a constant angular velocity (CAV) method or a zone constant angular velocity (ZCAV) method. Since DVDs are in the form of disks, the linear velocity increases from inside tracks to ouside tracks. It is, therefore, necessary to control the recording pulse length as well as recording power in order to adopt CAV or ZCAV system for spinning DVD-R disks.
It is an object of the present invention to provide an optical recording medium which has an organic dye-containing recording layer and which has a new wobbling format.
Another object of the present invention is to provide a DVD-R disk which does not require such fine control of cutting operation by a stamper as adopted in the case of land prepit format and which is adapted for a CAV or ZVAV disk spinning system.
It is a further object of the present invention to provide a DVD-R disk having improved light resistance.
It is yet a further object of the present invention to provide an optical recording method by multipulse recording or rectangular wave recording.
In accomplishing the above objects, the present invention provides an optical recording medium comprising a disk-like substrate and a recording layer provided over said substrate and containing at least one organic dye, said substrate having a wobble with a period length PL in the range of 4T to 96T.
In one embodiment, the recording layer contains at least two organic dyes one of which, when formed by itself into a film, has a maximum absorption wavelength greater than those of the other dyes and a refractive index greater than those of the other dyes.
In another embodiment, the recording layer, when formed by itself into a film, has a refractive index in the range of 1.5 to 3.0 and an extinction coefficient in the range of 0.02 to 0.2 both at a wavelength between xc2x15 nm from the reproducing wavelength.
In a further embodiment, the substrate has a groove depth d1 (xc3x85) satisfying the following relationship:
4000xe2x89xa6(d1)xc3x97(PL)xe2x89xa6240000 
where PL is as defined above.
In a further embodiment, the substrate has a wobble amplitude increasing in the radial direction.
In yet a further embodiment, the substrate has a guide groove depth increasing in the radial direction.